1. Field of the Invention
The present invention relates to a charging member to be used in an electrophotographic apparatus, and to a process cartridge and an electrophotographic apparatus each using the charging member.
2. Description of the Related Art
A charging member for charging an electrophotographic photosensitive member by abutting the photosensitive member is generally formed so as to have a rubber-containing elastic layer for securing a nip width between the photosensitive member and the charging member. As such elastic layer typically contains a low-molecular weight component, the low-molecular weight component may bleed to the surface of the charging member to adhere to the surface of the photosensitive member owing to long-term use. In addition, streak-like unevenness may appear in an electrophotographic image formed with the photosensitive member to which the low-molecular weight component has adhered.
In addition, such phenomenon occurs particularly remarkably when an electrophotographic image is formed with an electrophotographic apparatus left in a stop state under a high-temperature, high-humidity environment over a long time period.
To cope with such bleeding of a low-molecular weight component in an elastic layer, Japanese Patent Application Laid-Open No. 2001-173641 discloses a charging roll having an elastic layer whose peripheral surface is coated with an organic-inorganic hybrid coating so that the bleeding of a low-molecular weight component to its surface may be suppressed.
The inventors of the present invention have conducted investigations on the charging roll provided with the organic-inorganic hybrid coating described in Japanese Patent Application Laid-Open No. 2001-173641, and as a result, have found that the organic-inorganic hybrid coating has a small crosslink density. This is probably because emphasis is placed on the flexibility of the organic-inorganic hybrid coating. Accordingly, the inventors have acknowledged that the thickness of the organic-inorganic hybrid coating must be submicrons or more in order that the bleeding of the low-molecular weight component may be suppressed with reliability.
Here, the thickness of the surface layer of the charging member is preferably as small as possible from the viewpoint of charging efficiency. The thickness of the surface layer is preferably as small as possible from the viewpoint of the formation of a surface layer having a uniform thickness as well.